Apparatus for the weighted dosing of granulated or pulverulent products

ABSTRACT

Apparatus making it possible to effect accurately in line and continuously the weight feeding of granulated or pulverulent products. 
     It comprises two separated endless belts for extraction and dispensing. The endless belt of the dispenser is continuously weighed as a whole and the speed of the extraction apparatus is controlled to the measurement of the instantaneous load of product distributed on the dispenser belt. It comprises: 
     a hopper (2) for storing the product to be weighed under which is arranged an endless belt 3 for extraction of which one of the two support drums (5A, 5B) is driven at a variable speed by a motor-reduction gear, 
     a dispenser unit disposed below and in line with the endless belt 3 of the extractor, this unit being constituted of, 
     a fixed T-shaped support frame (9) which is provided at its ends with three pillars (10A-10B-10C) supporting three strain gauge type flexion weight indicators (11A-11B-11C) which are provided with flexible suspension cables (12A-12B-12C) to which is suspended an ultralight tubular frame (13) and, 
     an endless belt of which drums 14A-14B are supported by said frame 13, one of the drum 14A being driven at variable speed by a motor-reduction gear unit (16). 
     an electronic control chain F1-F2 between the motor-reductor gear unit (16) driving the endless belt (15) of the dispenser and the endless belt of the extractor (3) said chain being such that the speed of the endless belt of the extractor (3) is controlled in dependence to the measurement of the instantaneous load of product distributed on the dispenser belt (15). Application to the fertilizer industry.

The present invention relates generally to an improved apparatus makingit possible to effect accurately, in line and continuously, the weightfeeding or continuous mixing of a plurality of granulated or pulverulentproducts, such as: potassium chloride, sand, cement, phosphate,granules, and the like, this feeding generally being effected at thebeginning of a production process, for example in the fertilizerindustry, the cement and concrete industry, the agricultural foodstuffsindustry, and so on.

Apparatus already known make it possible to extract the product to beweighed from a hopper by means of a variable delivery extractionapparatus, to drop this extracted product on to the endless belt of adispenser, which is suspended and continuously weighed as a whole, todrive said dispenser belt at a determined speed corresponding to a givenprogrammed delivery of the dispenser, and controlling the speed of theextractor belt to the measurement of the instantaneous load of productdistributed on the dispenser belt.

In the apparatus known at present time use is made either of dispenserseffecting separate extraction or of single or double weighing rollersand integrating weighing machines.

Study of metrological criteria has led the Applicants to discardsingle-belt dispensers, which have serious disadvantages inasmuch as:

(a) Performance is modified by the dirtying of rollers, and by thespeed, tension and quality of the belt, as well as by the hopper load,

(b) Calibration is difficult and lengthy because it requires completeemptying of the hopper,

(c) The product weighing length is poorly defined.

Separate-extraction dispensers known at the present time consist of anendless belt receiving the product from an extractor disposed under ahopper, the entire belt arrangement being pivoted about a fixed axis andsuspended at its other end on a weight transducer, a counterweightoptionally being disposed opposite said transducer in order to balancethe dispenser under noload conditions. In other apparatus the endlessbelt of the dispenser is suspended at one arm of a balance, the otherarm bearing weights.

Whatever their mode of operation, these dispensers have disadvantages,such as lack of sensitivity around the fixed axis, the fact that theirperformance is modified by the quality and homogeneity of the belt.

The present invention concerns an apparatus making it possible to effectaccurately in line and continuously the weight feeding of granulated orpulverulent products comprising two separated endless belts forextraction and dispensing in which the endless belt of the dispenser iscontinuously weighed as a whole and in which the speed of the extractionapparatus is controlled to the measurement of the instantaneous load ofproduct distributed on the dispenser belt characterized in that itcomprises:

a hopper for storing the product to be weighed under which is arrangedan endless belt for extraction, of which one of the drums is driven atvariable speed by a motor-reduction gear.

a dispenser unit disposed below and in line with the extraction endlessbelt, this unit being constituted of a fixed T shaped support framewhich at its ends is provided with three pilars supporting three straingauge type flexion weight indicators which are provided with flexiblesuspension cables to which an ultralight tubular frame is attached anendless belt of which drums are supported by said ultralight tubularframe, one of the drums being driven at variable speed by amotor-reduction gear unit:

an electronic control chain between the motor-reduction gear unitdriving the endless belt of the dispenser and the motor-reduction gearunit of the endless belt of the extractor, said chain being such thatthe speed of the extraction apparatus is controlled in dependance to themeasurement of the instantaneous load of product distributed on thedispenser belt.

The apparatus of the present application provides substantial advantagesincluding the following:

the extraction apparatus can be optimized in accordance with theproduct,

accuracy is improved, particularly with low delivery, and may be as highas +0.2% of the delivery displayed,

there is a wide range of variation of the flow, which may extend from 5to 100% of rated delivery for one and the same dispenser,

the tension and quality of the belt used are immaterial,

perfect accessibility for cleaning and maintenance,

very slight deviation from calibration.

Other characteristics, advantages and features of the present inventionwill be clear from the description of the latter which is given belowwith reference to the accompanying drawings showing, diagrammaticallyand simply, one possible embodiment of the invention which is given as apreferred exmaple.

In these drawings,

FIG. 1 is a diagram showing in elevation a continuous meteringarrangement applying the process according to the invention,

FIGS. 2 and 3 are detail views on a larger scale, showing, in elevationand in plan respectively, the actual dispenser, and

FIG. 4 is a basic diagram of the regulation and operation of thecontinuous weight feeding installation utilizing the process accordingto the invention.

Referring firstly to FIG. 1, it can be seen that in accordance with theinvention the product 1 to be dispensed is stored in a hopper 2, belowwhich is disposed an endless belt type extractor 3. This belt issupported by drive and return drums 5A, 5B and is driven at variablespeed by a direct-current laminated-winding motor-reduction gear unitwhich is provided with a speed takeoff and is given the generalreference 4, and which acts on the front drive drum 5A of the extractorbelt.

A manually or automatically controlled hood 6 is disposed at the end ofthe extractor for the purpose of regulating the height of the layer ofproduct 1 extracted from the hopper 2 by the belt 3.

A series of chains 7 is disposed transversely of the belt 3, justupstream of the point where the product drops. These chains, whichconstitute a sort of transverve curtain, serve the purpose ofregularizing the delivery and fractionating the product in order toreduce the effect of the fall onto the actual dispenser unit, which isgiven the general reference 8 and is disposed under and in line with theextractor belt 3.

This dispenser unit 8 (see also FIGS. 2 and 3) is composed of a fixedT-shaped support frame 9, which at its ends is provided with threepillars 10A, 10B, 10C supporting three strain gauge type flexion weightindicators, which are provided with flexible suspension cables 12A, 12B,12C to which an ultralight tubular frame 13 is attached.

This suspended tubular frame serves as support for drive and returndrums 14A, 14B of an endless belt forming a dispenser belt 15 and isdriven at variable speed by a direct-current laminated-windingmotor-reduction gear unit provided with a speed takeoff and given thegeneral reference 16.

In order that the weighing length may be accurately delimited, athrowing table 17 is disposed at the rear part of the tubular frame 13which is situated under the extractor belt 3, for the purpose ofreceiving the product 1 thrown back by the latter, while a transversecurtain of chains 18 is installed at the outlet of the belt 15 of thedispenser and serves the purpose of always fractionating the product atthe same spot and throwing it back in the direction of the arrow Ftowards a collector belt 20 for the continuation of the treatment of theproduct.

In addition, the belt 15 of the dispenser slides over a series ofupwardly inclined self-sliding carrier troughs 19, which raise the edgesof the belt 15 of the dispenser along all the part where weighing iseffected. It can be seen that the dispenser belt 15 which receives theproduct 1 (from the extractor belt 3) transports this product to theoutlet while constantly effecting the instantaneous integral weighing bymeans of the system comprising the weight indicators 11A, 11B, 11C overa very precise length.

The dispenser belt 15 is driven by its motor 16 at a determined speedcorresponding to a given programmed delivery of the dispenser unit 8.

According to an essential characteristic of the process of the inventionthe speed at which the extractor belt 3 is driven by its motor 4 iscontrolled in dependence to the measurement of the instantaneous load ofproduct distributed on the dispenser belt, this being achieved by meansof a control chain indicated schematically by the double arrow F1-F2 inFIG. 1, this being done in such a manner that if the measurement of theinstantaneous load of product distributed over the extractor belt 15does not correspond to the individual set point of the dispenser unit 8,the speed of the extractor belt 3 will be automatically corrected in theupward or downward direction so as to keep the load of product constantwhatever the programmed delivery of the dispenser.

Referring now more particularly to FIG. 4, a description will be givenvery briefly to explain how, as an example, the control chain (F1-F2)may be constructed for controlling the speed of the extractor belt 3 independence on the measurement of the instantaneous load of productdistributed on the dispenser belt and correcting it so that the load ofproduct on the dispenser belt will remain constant whatever theprogrammed delivery of the dispenser.

For this purpose the electrical part is composed of three interdependentlooped control chains and two digital computers with their ancillaryequipment.

The complete control system comprises:

(a) a loop controlling the speed of the belt 15 of the dispenser,

(b) a weight control loop, and

(c) a loop controlling the speed of the extractor belt.

The first loop (a) enables the linear speed of the belt 15 of thedispenser to be controlled (with an accuracy of +1/1000) in dependenceon the individual programmed delivery set point of the dispenser.

This individual programmed delivery set point of the dispenser isdisplayed in clear in tonnes per hour on a digital display 21, and isthe result of a calculation made on the basis of the two signals,namely:

1. The general set point signal of all the dispensers of aninstallation, this digital signal expressed in tonnes per hour beingworked out from a keyboard 22'.

2. The signal originating from the dispenser concerned, which is aproportion and constitutes the individual set point associated with thatdispenser and expressed in kilograms per tonne of the final product,this signal being worked out with the aid of code wheels and displayedon a display 23'.

These two signals are fed to the inputs on a first digital computer 24,which effects the following operation: (general set point int/h)×(proportion corresponding to the dispenser in kg/t)=programmeddelivery set point in kg/h.

As a numerical example, it may be mentioned that the exemplifieddispensing installation has in particular been used with a general setpoint of 32 t/h and an individual set point of the respective dispenserof 110 kg/t, which corresponds to a programmed delivery set point of3520 kg/h.

This programmed delivery set point is on the one hand displayed on thedigital display 21, and on the other hand controls the speed variator16A of the motor-reduction gear unit 16 of the dispenser.

The controller of this variator permanently maintains the speedstability of the motor 16 driving the drum 14A of the dispenser 15 bycomparing the programmed delivery set point 21 with the actual speedmeasurement supplied by the transducer 16B mounted in themotor-reduction gear unit.

The second control loop, the weight control loop (b), makes it possibleto control and accurately maintain a constant load of product on thedispenser, whatever the programmed delivery, that is to say whatever thespeed of the dispenser belt.

For this purpose a weight controller 22, which has a preprogrammedinternal set point, is provided.

In addition, the actual instantaneous measurement of the weight on thedispenser, originating from the signal of the three strain gauges 11A,11B, 11C mounted in parallel, is amplified and filtered by means of aweight transmitter 23, and is fed to the weight controller 22 which hasa preprogrammed set point.

When the difference between this set point and the actual instantaneousmeasurement of the weight on the dispenser, originating from the weighttransmitter, is not zero, the controller will supply a positive ornegative correction signal to the speed variator 4A of themotor-reduction gear unit 4 driving the drum 5A of the extractor belt 3,which has the effect of increasing or reducing the amount of productreaching the dispenser, in order to eliminate the weight differencedetected.

It is important to note that when the dispenser is empty, on commencingoperation, the output signal of this controller is masked by that of aramp generator, which has the effect of gradually and uniformly loadingthe dispenser; when the weight on the dispenser corresponds to thepreprogrammed internal set point, the controller takes over andmaintains a constant weight on the dispenser.

The third control loop (c), controlling the speed of the extractionbelt, makes it possible to control accurately the linear speed of theextractor belt in dependence on the correction signal given by theweight controller 22.

For this purpose this weight controller 22, as has been seen, providesat its output positive or negative corrective set point steps which arefirst mixed with the set point signal of the programmed delivery of thedispenser from the first loop (a). The signal produced by this mixingserves as set point for the speed variator 4A of the extractor beltmotor 4.

The controller of this variator therefore continuously adjusts the speedof the extractor motor by comparing this correction set point with theactual speed measurement supplied by the speed transducer 4B installedin the motor-reduction gear unit.

A second computer incorporated in the weight controller 22 serves thepurpose of effecting the following calculation.

(Actual instantaneous delivery)=(actual instantaneous weight on thedispenser)×(actual instantaneous speed of the dispenser belt).

For this purpose the weight information coming from the weighttransmitter 23 is fed to one of the inputs of the computer, while thespeed information coming from the speed transducer 16B installed in themotor-reduction gear unit of the dispenser belt 15 arrives in codeddigital form and is fed to the other input of the computer.

The result of this calculation of the actual instantaneous deliverycalculation is directly displayed in clear on a digital display 24'.

The operator is therefore able to check by a single glance the correctoperation of the dispenser by comparing the readings of the twodisplays: the delivery set point 21 and the actual instantaneousdelivery 24'; in normal operation these displays should be identical.

This computer 22 also enables counting and control of alarms to becarried out with the aid of the two electronic circuits.

For counting purposes the linear actual instantaneous delivery outputsignal is converted into a proportional pulse signal permitting theoutputting of a signal complying with requirements, that is to say onepulse per unit of product treated, for example one pulse per 100 g orone pulse per 1 kg, and so on.

This adapted signal is then counted and stored in a digital counter 25enabling the amount of product passed to be known.

For the purpose of alarm control, the actual instantaneous deliverysignal is compared with the delivery set point signal 21 of thedispenser. The comparator has two adjustable alarm thresholds, forexample at +2%; if the signal passes one of these two thresholds, acontrol circuit 26 will, at the end of a given period of time, operate alight and/or acoustic alarm relay, and, at the end of a given longerperiod of time, another relay effecting the disconnection of the generalset point of the dispensing installation.

Suitable instructions can be given to the computer 22 at 27.

It is obvious that the present invention has been described andillustrated only in respect of a preferred example, and that technicalequivalents could be used for its component parts without departing fromits scope.

I claim:
 1. Apparatus making it possible to effect accurately in lineand continuously the weight feeding of granulated or pulverulentproducts comprising two separated endless belts for extracting anddispensing, in which the endless belt of the dispenser is continuouslyweighed as a whole and in which the speed of the extraction apparatus iscontrolled to the measurement of the instantaneous load of productdistributed on the dispenser belt characterized in that it comprises:ahopper (2) for storing the product to be weighed under which is arrangedan endless belt (3) for extraction, of which one of the two supportdrums (5A, 5B) is driven at a variable speed by a motor-reduction gear(4), a dispenser unit (8) disposed below and in line with the endlessbelt (3) of the extractor, this unit being constituted of a fixedT-shaped support frame (9) which is provided at its ends with threepillars (10A-10B-10C) supporting three strain gauge type flexion weightindicators (11A, 11B, 11C) which are provided with flexible suspensioncables (12A, 12B, 12C), an ultralight tubular frame (13), an endlessbelt (15) of which drums (14A-14B) are supported by said frame (13), oneof the drums (14A) being driven at variable speed by a motor-reductiongear unit (16), an electronic control chain F1-F2 between the motorreductor gear unit (16) driving the endless belt (15) of the dispenserand the motor gear unit (4) of the endless belt of the extractor (3),said chain being such that the speed of the endless belt of theextractor (3) is controlled in dependence to the measurement of theinstantaneous load of product distributed on the dispenser belt (15). 2.Apparatus according to claim 1 characterized in that transverse curtainsof chains (7-18) are disposed just upstream of the point where theproduct is dropped, for the purpose of regularizing the delivery of theproduct both onto the extraction apparatus (3) and onto the dispenser(8) and fractionating said product and reducing the effect of the dropat the outlets of these apparatus.
 3. Apparatus according to claim 1 or2 characterized in that the motor-reduction gear units (4, 16) of theextraction apparatus (3) and of the dispenser (8) are direct-currentlaminated-winding units provided with a speed takeoff.
 4. Apparatusaccording to claim 1 characterized in that the electronic part of thesystem controlling the speed of the extraction apparatus (3) independence on the measurement of the instantaneous load on the dispenserbelt (15) is composed of three looped interdependent control chains andtwo digital computers with their ancillary equipment; a first looppermitting control of the linear speed of the dispenser belt (15) independence on the individual programmed delivery set point of thedispenser (8) and containing a computer (24) whose output signalcontrols the speed variator (16A) of the motor-reduction gear unit (16)of the dispenser, the controller of this variator permanentlymaintaining the speed stability of the motor (16') by comparing theprogrammed delivery set point (21) with the actual measurement of speedsupplied by the speed transducer (16B) installed in the motor-reductiongear unit (16); a second loop making it possible to control andaccurately maintain a constant load of product on the dispenser whateverthe programmed delivery, this loop containing a weight controller (22)having a preprogrammed delivery internal weight set point and receivingthe actual instantaneous measurement of the weight on the dispenser froma weight transmitter (23) receiving the signals from the strain gauges(11A-11B-11C), said weight controller (22) supplying, in dependence onthe difference between said prepogrammed set point and said actualinstantaneous measurement, a positive or negative correction signal tothe speed variator (4A) of the motor-reduction gear unit (4) of theextraction apparatus (3); a third loop making it possible to controlaccurately the linear speed of the extraction apparatus (3) independence on the correction signal supplied by the weight controller(22), which signal is mixed with the programmed delivery set pointsignal of the dispenser in the first loop and is fed as correction setpoint to the variator (4A) of the motor-reduction gear unit (4) of theextraction apparatus (3), the controller of this variator permanentlyadjusting the speed stability of the motor (4) by comparing thecorrection set point with the actual speed measurement supplied by thespeed transducer (4B) installed in the motor-reduction gear unit (4). 5.Apparatus according to claim 4 characterized in that when the dispenseris empty, on starting up, the output signal of the weight controller(22) is masked by the signal of a ramp generator which has the effect ofgradually and uniformly loading the dispenser belt (15), and that whenthe weight on the dispenser belt (15) corresponds to the internalpreprogrammed set point in the controller (22), the latter takes overand maintains a constant weight on the dispenser belt (15).
 6. Apparatusaccording to claim 5 characterized in that a second computer serves thepurpose of making the calculation:(Actual instantaneousdelivery)=(actual instantaneous weight on the dispenser belt)×(actualinstantaneous speed of the dispenser belt), the weight informationcoming from the weight transmitter (23) being fed to one of the inputsof the computer, while the speed information coming from the speedtransducer (16B) installed in the motor-reduction gear unit of thedispenser belt (15) arrives in coded digital from and is fed to theother input of the computer, as the consequence of which the result ofthis actual instantaneous delivery is directly displayed in clear on adigital display (24) and, then compared with the delivery set point (21)of the dispenser, makes it possible to check that the dispenser plant(8) is working normally.
 7. Apparatus according to claim 6 characterizedin that the actual instantaneous delivery output signal of the secondcomputer is processed by two electronic circuits: in the first, which isused for counting, the linear actual instantaneous delivery signal isconverted into a proportional pulse signal, one pulse per unit ofproduct dispensed, and is counted and stored in a digital counter (25)making it possible to ascertain the amount of product passed; in thesecond, which is used for control of alarms, the actual instantaneousdelivery signal is compared with the delivery set point (21) signal ofthe dispenser in a comparator having two adjustable alarm thresholds,and if one of these thesholds is passed an alarm control circuit (26)will, at the end of a given period of time, operate a light and/oracoustic alarm relay and, at the end of a given longer period of time,another relay controlling the general disconnection of the dispensingplant.